Systemic sclerosis (SSc) and ankylosing spondylitis (AS) are two immune-mediated diseases, the former an autoimmune disease associated with specific alleles of HLA class II DR, DQ and DP, and the latter an autoinflammatory disease associated with HLA class I alleles, most specifically HLA-B27. However, the MHC contribution to neither disease can be fully explained by associations with only these classic HLA alleles. Recent genome-wide association studies (GWAS) conducted by us have shown that the strongest disease-association loci fall within the major histocompatibility complex (MHC) in both diseases. Polymorphisms of multiple classic and non-classic HLA genes within the HLA region displayed significant associations with each of the diseases. These observations suggest that some non-classic HLA gene variants also may contribute to susceptibility to or protection from these two diseases. However, because of the extensive linkage disequilibrium (LD) between genes within the HLA region, some of observed disease associations may be due to LD. Alternatively, multiple true MHC associations may additively heighten or lower disease risk. To circumvent this problem, we propose herein to examine these candidate genes identified from the GWAS with deep sequencing in three distinct ethnic groups. Sequencing candidate genes will provide the highest resolution for viewing genetic polymorphisms that can be used to construct comprehensive haplotype combinations, as well as to identify rare alleles. Subsequently, identified haplotypes and rare alleles will be examined in different ethnic groups for confirmation in an effort to locate causative gene variants to the diseases. The overall long-term objective of this proposal is to define the roles of specific HLA-region gene variations in susceptibility to or protection from SSc and AS, as well as in association with specific clinical presentations, disease subgroups and/ or severity. Information obtained from these studies will ultimately lead to understanding of disease pathogenesis and development of target specific therapies in SSc and AS. This proposal will fulfill the mission of the FOA to study HLA region genomics in immune-mediated diseases.